Barium complexes cryptands

Purex process, 6,940 Barium, pentakis(diacetamide)-stereochemistry, 1, 99 Barium alkoxides synthesis, 2,336 Barium complexes cryptands, 3,53 phthalocyanines, 2, 863 porphyrins, 2,820 pyridine oxide, 3,9 urea, 3,9... 

Barium complexes cryptands, 53 pyridine oxide, 9 urea,9 Beauveracin... 

In order to accommodate the small, highly charged calcium ion, the cryptand adopts an unsymmetrical conformation in which two of the chains are pushed apart to allow coordination of a water molecule and the N N distance is reduced to 5.44 A (42). In the corresponding barium complex, the structural unit consists of two cryptates, two water molecules, and four thiocyanate anions, two of which (9) are bound through nitrogen to the metal, (43). 

A plethora of crown ether- or cryptand type molecules have been reported. Some of them are depicted below to show their diversity and versatility. Lariat azaether containing cyclen macrocycle 208 [36] and azaethers involving triazole 209 [37], furane or pyrrole containing macrocycles which can complex two copper 210 [38] or one barium cations 211 [39], spiro-linked crown ethers 212 [40] andcagecompounds 213 [41] which, in addition to two alkali cations, could... 

The number of donor atoms can be influential in complex formation. Ideally, as the incoming ligand is comparable to an inner solvation sphere, the number of donor atoms should match the preferred coordination number of the cation. An example of this factor comes from a comparison of two similarly sized ligands, [2.2.2]cryptand and [2.2.C8]cryptand, the latter having one dioxoether chain replaced by a C8 unit.478 A reversal of the Ba2+/K+ selectivity of the order of 106 is found, the ratio being 104 for [2.2.2]cryptand and <10 2 for [2.2.C8]cryptand the preferred coordination numbers are six for potassium and eight for barium. 

The effect of cation-complexing agents on the barium(II)-assisted basic ethanolysis of phenyl acetate has been looked at.184 Addition of various crown ethers yields ternary complexes of 1 1 1 crown-metal-ethoxide composition and a definite cation activation takes place. Cryptand 222 removes the catalytic activity. 

Ligand 131 contains both cryptate and crown ether binding units. It reacts with neodymium triflate to give a 1 1 cryptate [Nd c 131]3+ exhibiting NIR luminescence upon excitation at 355 nm. The lifetime of the Nd(4F3/2) level is 347 and 711 ns in methanol and methanol-, respectively, which translates to MeOH 0 using eq. (10b). When barium ions are added to a solution of this complex in acetonitrile, the intensity of the 1.06 pm emission band is reduced substantially, while the lifetime of the Nd(4F3/2) level remains unchanged at about 470 ns. The Ndm ion is therefore not displaced from the cryptand cavity, while its luminescence is modulated by the presence of the Ba2+ ions bound by the crown ether (Coldwell et al., 2006). 

Although not particularly designed to be a pH-sensitive luminescent probe, Beeby et al. described a phenanthridine-carrying water-soluble Yb complex, in which the photosensitisation mechanism is switched as a functi(m of pH [93], A crown ether-modified neodymium(III) cryptand was proposed for barium ion detection [94], but as with many prototype cation sensors, the probe only works in acetonitrile. Moreover, the complex necessitates ultraviolet excitation, which removes one of the main advantages of using NIR luminescent lanthanide complexes. 

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